U.S. patent application number 15/627493 was filed with the patent office on 2018-02-01 for fabrication method of strontium niobium oxynitride film having small carrier density and its use.
The applicant listed for this patent is Panasonic Corporation. Invention is credited to KAZUHITO HATO, RYOSUKE KIKUCHI, TORU NAKAMURA.
Application Number | 20180030602 15/627493 |
Document ID | / |
Family ID | 61009362 |
Filed Date | 2018-02-01 |
United States Patent
Application |
20180030602 |
Kind Code |
A1 |
KIKUCHI; RYOSUKE ; et
al. |
February 1, 2018 |
FABRICATION METHOD OF STRONTIUM NIOBIUM OXYNITRIDE FILM HAVING
SMALL CARRIER DENSITY AND ITS USE
Abstract
The present invention provides a method for growing a strontium
niobium oxynitride film, the method comprising: (a) growing, on a
strontium titanate substrate, by a sputtering method, the strontium
niobium oxynitride film having carrier density of not more than
1.times.10.sup.18 cm.sup.-3. The spirit of the present invention
includes: (I) strontium niobium oxynitride having carrier density
not more than 1.times.10.sup.18 cm.sup.-3, (II) a strontium niobium
oxynitride film having carrier density not more than
1.times.10.sup.18 cm.sup.-3, (III) a photosemiconductor substrate
comprising the strontium niobium oxynitride film, (IV) a hydrogen
generation device comprising the photosemiconductor substrate, and
(V) a hydrogen generation method using the photosemiconductor
substrate. The present invention provides a fabrication method of a
strontium niobium oxynitride film having small carrier density and
its use.
Inventors: |
KIKUCHI; RYOSUKE; (Osaka,
JP) ; NAKAMURA; TORU; (Osaka, JP) ; HATO;
KAZUHITO; (Osaka, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Panasonic Corporation |
Osaka |
|
JP |
|
|
Family ID: |
61009362 |
Appl. No.: |
15/627493 |
Filed: |
June 20, 2017 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
Y02E 60/364 20130101;
C25B 1/04 20130101; C25B 11/0447 20130101; C25B 1/003 20130101;
C23C 14/3457 20130101; C25B 9/06 20130101; C23C 14/3414 20130101;
C23C 14/0036 20130101; Y02E 60/36 20130101; C25B 11/0405 20130101;
Y02E 60/366 20130101; C25B 11/0415 20130101; C23C 14/0676 20130101;
C23C 14/3407 20130101 |
International
Class: |
C25B 1/00 20060101
C25B001/00; C23C 14/34 20060101 C23C014/34; C23C 14/00 20060101
C23C014/00; C25B 11/04 20060101 C25B011/04; C25B 9/06 20060101
C25B009/06; C23C 14/06 20060101 C23C014/06; C25B 1/04 20060101
C25B001/04 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 28, 2016 |
JP |
2016-148096 |
Claims
1. A method for growing a strontium niobium oxynitride film, the
method comprising: (a) growing, on a strontium titanate substrate,
by a sputtering method, the strontium niobium oxynitride film
having carrier density of not more than 1.times.10.sup.18
cm.sup.-3.
2. The method according to claim 1, wherein a target used in the
sputtering method is formed of strontium niobate; and the strontium
niobium oxynitride film is grown in an atmosphere containing
nitrogen.
3. The method according to claim 2, wherein the strontium niobate
is represented by the chemical formula Sr.sub.2Nb.sub.2O.sub.7.
4. The method according to claim 2, wherein the atmosphere further
contains oxygen.
5. The method according to claim 2, wherein the atmosphere further
contains argon.
6. The method according to claim 4, wherein the atmosphere further
contains argon.
7. The method according to claim 1, wherein the strontium titanate
substrate has a single orientation plane; and the strontium niobium
oxynitride film has a single orientation plane.
8. The method according to claim 7, wherein the single orientation
plane of the strontium titanate substrate is an orientation plane
of a (001) plane; and the single orientation plane of the strontium
niobium oxynitride film is an orientation plane of a (001)
plane.
9. The method according to claim 7, wherein the single orientation
plane of the strontium titanate substrate is an orientation plane
of a (110) plane; and the single orientation plane of the strontium
niobium oxynitride film is an orientation plane of a (110)
plane.
10. The method according to claim 7, wherein the single orientation
plane of the strontium titanate substrate is an orientation plane
of a (111) plane; and the single orientation plane of the strontium
niobium oxynitride film is an orientation plane of a (111)
plane.
11. The method according to claim 1, wherein the strontium titanate
substrate is doped with at least one selected from the group
consisting of niobium and lanthanum.
12. A strontium niobium oxynitride having carrier density of not
more than 1.times.10.sup.18 cm.sup.-3.
13. The strontium niobium oxynitride according to claim 12, wherein
the carrier density is not more than 1.times.10.sup.17
cm.sup.-3.
14. A strontium niobium oxynitride film having carrier density of
not more than 1.times.10.sup.18 cm.sup.-3.
15. The strontium niobium oxynitride film according to claim 14,
wherein the carrier density is not more than 1.times.10.sup.17
cm.sup.-3.
16. The strontium niobium oxynitride film according to claim 14,
wherein the strontium niobium oxynitride film has a single
orientation plane.
17. The strontium niobium oxynitride film according to claim 16,
wherein the single orientation plane is an orientation plane of a
(001) plane.
18. The strontium niobium oxynitride film according to claim 16,
wherein the single orientation plane is an orientation plane of a
(110) plane.
19. The strontium niobium oxynitride film according to claim 16,
wherein the single orientation plane is an orientation plane of a
(111) plane.
20. A semiconductor photoelectrode comprising: a strontium titanate
substrate; and a strontium niobium oxynitride film grown on the
strontium titanate substrate, wherein the strontium niobium
oxynitride film has carrier density of not more than
1.times.10.sup.18 cm.sup.-3.
21. The semiconductor photoelectrode according to claim 20, wherein
the carrier density is not more than 1.times.10.sup.17
cm.sup.-3.
22. The semiconductor photoelectrode according to claim 20, wherein
the strontium titanate substrate has a single orientation plane;
and the strontium niobium oxynitride film has a single orientation
plane.
23. The semiconductor photoelectrode according to claim 20, wherein
the strontium titanate substrate is doped with at least one
selected from the group consisting of niobium and lanthanum.
24. A hydrogen generation device, comprising: a semiconductor
photoelectrode according to claim 20; a counter electrode
electrically connected to the semiconductor photoelectrode; a
liquid in contact with the strontium niobium oxynitride film and
the counter electrode; and a container containing the semiconductor
photoelectrode, the counter electrode, and the liquid, wherein the
liquid is water or an electrolyte aqueous solution; and hydrogen is
generated on a surface of the counter electrode when the strontium
niobium oxynitride film is irradiated with light.
25. The hydrogen generation device according to claim 24, wherein
the carrier density is not more than 1.times.10.sup.17
cm.sup.-3.
26. The hydrogen generation device according to claim 24, wherein
the strontium titanate substrate has a single orientation plane;
and the strontium niobium oxynitride film has a single orientation
plane.
27. The hydrogen generation device according to claim 26, wherein
the strontium titanate substrate is doped with at least one
selected from the group consisting of niobium and lanthanum.
Description
BACKGROUND
1. Technical Field
[0001] The present invention relates to a fabrication method of a
strontium niobium oxynitride film having small carrier density and
its use.
2. Description of the Related Art
[0002] NPL1 discloses that strontium niobium oxynitride represented
by the chemical formula SrNbO.sub.2N absorbs light having a
wavelength of not more than 700 nanometers. Strontium niobium
oxynitride is one kind of a perovskite niobium oxynitride.
Furthermore, NPL1 discloses a semiconductor photoelectrode
fabrication method in which SrNbO.sub.2N particles are deposited on
a fluorine-doped tin oxide substrate by an electrophoretic
deposition method. According to NPL1, the thus-fabricated
semiconductor photoelectrode is irradiated with light to generate
oxygen due to water splitting on the surface of the semiconductor
photoelectrode.
[0003] NPL2 discloses a method for growing a SrNbO.sub.3-xN.sub.x
film (0.ltoreq.x.ltoreq.1) by a pulse laser deposition method on a
KTaO.sub.3 single-crystal substrate having an orientation plane of
a (100) plane. According to NPL2, the thus-grown
SrNbO.sub.3-xN.sub.x film has carrier density of not less than
1.times.10.sup.21 cm.sup.-3.
[0004] NPL3 discloses a method for growing a SrTaO.sub.3-xN.sub.x
film (0.ltoreq.x.ltoreq.1.2) by a pulse laser deposition method on
a SrTiO.sub.3 single-crystal substrate having an orientation plane
of a (100) plane. NPL3 does not disclose the carrier density of the
thus-grown SrTaO.sub.3-xN.sub.x film.
CITATION LIST
[0005] NPL1: Kazuhiko Maeda et al, "SrNbO.sub.2N as a
Water-Splitting Photoanode with a Wide Visible-Light Absorption
Band", Journal of the American Chemical Society, vol. 133, pp.
12334-12337 (2011)
[0006] NPL2: Daichi Oka et. al., `Electric Transport Properties of
Nb-based perovskite oxynitride epitaxial thin films", Proceedings
of The 61st Japan Society of Applied Physics Spring Meeting, 2014,
18p-E8-13, 06-149.
[0007] NPL3: Daichi Oka et. al., "Possible ferroelectricity in
perovskite oxynitride SrTaO.sub.2N epitaxial thin films",
Scientific Reports, Vol. 4, pp 4987 (2014)
SUMMARY
[0008] An object of the present invention is to provide a
fabrication method of a strontium niobium oxynitride film having
small carrier density and its use.
[0009] The present invention provides a method for growing a
strontium niobium oxynitride film, the method comprising:
[0010] (a) growing, on a strontium titanate substrate, by a
sputtering method, the strontium niobium oxynitride film having
carrier density of not more than 1.times.10.sup.18 cm.sup.-3.
[0011] The spirit of the present invention includes:
[0012] (I) strontium niobium oxynitride having carrier density not
more than 1.times.10.sup.18 cm.sup.-3, and
[0013] (II) a strontium niobium oxynitride film having carrier
density not more than 1.times.10.sup.18 cm.sup.-3.
[0014] The spirit of the present invention further includes:
[0015] (III) a photosemiconductor substrate comprising the
strontium niobium oxynitride film,
[0016] (IV) a hydrogen generation device comprising the
photosemiconductor substrate, and
[0017] (V) a hydrogen generation method using the
photosemiconductor substrate.
[0018] The present invention provides a fabrication method of a
strontium niobium oxynitride film having small carrier density and
its use.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] FIG. 1 shows a cross-sectional view of a semiconductor
photoelectrode 100.
[0020] FIG. 2 is a graph showing an X-ray diffraction measurement
result in the inventive example 1.
[0021] FIG. 3 is a graph showing an X-ray diffraction measurement
result in the inventive example 2.
[0022] FIG. 4 shows a cross-sectional view of a hydrogen generation
device comprising the semiconductor photoelectrode 100.
[0023] FIG. 5 shows a cross-sectional view of the semiconductor
photoelectrode 100.
[0024] FIG. 6 is a graph showing an X-ray diffraction measurement
result in the inventive example 3.
[0025] FIG. 7 is a graph showing an X-ray diffraction measurement
result in the inventive example 4.
DETAILED DESCRIPTION OF THE EMBODIMENT
[0026] Hereinafter, the embodiment of the present invention will be
described with reference to the drawings.
[0027] (Embodiment)
[0028] FIG. 1 shows a cross-sectional view of a semiconductor
photoelectrode 100 according to the embodiment. The semiconductor
photoelectrode 100 comprises a strontium titanate substrate 110
(hereinafter, referred to as "substrate 110") and a strontium
niobium oxynitride film 120. The substrate 110 may include another
layer, as far as the surface of the substrate 110 is formed of
strontium titanate. Desirably, the substrate 110 is single-crystal.
The strontium titanate is represented by the chemical formula
SrTiO.sub.3. The strontium niobium oxynitride may be represented by
the chemical formula SrNbO.sub.3-xN.sub.x (where x is more than 0
and not more than 3, desirably, x=1). The strontium niobium
oxynitride is one kind of n-type semiconductors.
[0029] The strontium niobium oxynitride film 120 is formed on the
surface of the substrate 110. Desirably, the strontium niobium
oxynitride film 120 has an orientation plane. More preferably, the
strontium niobium oxynitride film 120 has an orientation plane of a
(001) plane.
[0030] (Fabrication Method)
[0031] A fabrication method according to the present embodiment
will be described below.
[0032] While the temperature of the substrate 110 is maintained at
not less than 500 degrees Celsius and not more than 750 degrees
Celsius, the strontium niobium oxynitride film 120 is grown on the
substrate 110. The substrate 110 is formed of strontium titanate,
as described above. It is desirable that the substrate 110 is
formed of single-crystal strontium titanate. It is desirable that
the grown strontium niobium oxynitride film 120 has an orientation
plane.
[0033] It is desirable that the substrate 110 has a principal
surface of a (001) plane, a (110) plane, or a (111) plane. In other
words, it is desirable that the surface of the substrate 110 formed
of strontium titanate is oriented in a [001] direction, a [110]
direction, or a [111] direction. It is more desirable that the
substrate 110 comprises strontium titanate having only an (001)
orientation plane, only an (110) orientation plane, or only an
(111) orientation plane on the surface thereof.
[0034] The present inventors found that a strontium niobium
oxynitride film grown by a sputtering method has significantly
lower carrier density than a strontium niobium oxynitride film
grown by a pulse laser deposition method. Specifically, the
strontium niobium oxynitride film grown by a laser deposition
method has high carrier density of not less than 1.times.10.sup.21
cm.sup.-3 (See NPL2), whereas the strontium niobium oxynitride film
grown by a sputtering method has low carrier density of not more
than 1.times.10.sup.18 cm.sup.-3, as demonstrated in the inventive
examples which will be described later. In one embodiment, the
strontium niobium oxynitride film grown by a sputtering method has
low carrier density of not more than 1.times.10.sup.17 cm.sup.-3.
As will be described later, the low carrier density improves
hydrogen generation efficiency.
[0035] In the sputtering method, it is desirable that a target
formed of strontium niobate represented by the chemical formula
Sr.sub.2Nb.sub.2O.sub.7 is used. Sputtering is carried out in an
atmosphere of a mixture of argon and nitrogen. It is desirable that
the atmosphere further contains oxygen. In this way, the strontium
niobium oxynitride film 120 is grown on the substrate 110.
[0036] When the substrate 110 has an orientation plane of a (001)
plane, the strontium niobium oxynitride film 120 also has an
orientation plane of a (001) plane. It is more desirable that the
strontium niobium oxynitride film 120 has a (001) orientation only.
Likewise, when the substrate 110 has an orientation plane of a
(110) plane, the strontium niobium oxynitride film 120 also has an
orientation plane of a (110) plane. In this case, it is more
desirable that the strontium niobium oxynitride film 120 has a
(110) orientation only. When the substrate 110 has an orientation
plane of a (111) plane, the strontium niobium oxynitride film 120
also has an orientation plane of a (111) plane. In this case, it is
more desirable that the strontium niobium oxynitride film 120 has a
(111) orientation only.
[0037] The strontium niobium oxynitride film 120 grown in this way
has low carrier density of not more than 1.0.times.10.sup.13
cm.sup.-3, as described above.
[0038] FIG. 4 shows a cross-sectional view of a hydrogen generation
device 600 comprising the semiconductor photoelectrode 100. In the
present embodiment, the semiconductor photoelectrode 100 comprises
the strontium niobium oxynitride film 120. The strontium niobium
oxynitride is a photosemiconductor and can be used as a
photocatalyst. The hydrogen generation device shown in FIG. 4
comprises the semiconductor photoelectrode 100, a counter electrode
630, a liquid 640, and a container 610. As described above, the
semiconductor photoelectrode 100 comprises the substrate 110 and
the strontium niobium oxynitride film 120 grown on the substrate
110.
[0039] FIG. 5 shows a cross-sectional view of the semiconductor
photoelectrode 100. The strontium titanate substrate 110 doped with
niobium or lanthanum may be used. The strontium titanate substrate
110 doped with niobium or lanthanum is electrically conductive. As
shown in FIG. 5, an ohmic electrode 111 may be formed on the
conductive strontium titanate substrate 110. The ohmic electrode
111 is electrically connected to a conducting wire 650. The
substrate 110 is a perovskite (e.g., a perovskite oxide).
[0040] It is desirable that the counter electrode 630 is formed of
a material having a small overvoltage on the hydrogen generation
reaction. Alternatively, it is desirable that the counter electrode
630 may be formed of a semiconductor photoelectrode capable of
generating hydrogen. In particular, an example of the material of
the counter electrode 630 is platinum, gold, silver, nickel,
ruthenium oxide represented by the chemical formula RuO.sub.2,
iridium oxide represented by the chemical formula IrO.sub.2, or a
p-type semiconductor. Two or more materials may be used for the
counter electrode 630.
[0041] The liquid 640 is water or an electrolyte aqueous solution.
The electrolyte aqueous solution is acidic or alkaline. An example
of the electrolyte aqueous solution is a sulfuric acid aqueous
solution, a sodium sulfate aqueous solution, a sodium carbonate
aqueous solution, a phosphate buffer solution, or a borate buffer
solution. The liquid 640 may be constantly stored in the container
610 or may be supplied only in use.
[0042] The container 610 contains the semiconductor photoelectrode
100, the counter electrode 630, and the liquid 640. It is desirable
that the container 610 is transparent. In particular, it is
desirable that at least a part of the container 610 is transparent
so that light can travel from the outside of the container 610 to
the inside of the container 610. A user of the hydrogen generation
device 600 prepares such a hydrogen generation device 600.
[0043] When the strontium niobium oxynitride film 120 is irradiated
with light, oxygen is generated on the surface of the strontium
niobium oxynitride film 120. Light such as sunlight travels through
the container 610 and reaches the strontium niobium oxynitride film
120. Electrons and holes are generated respectively in the
conduction band and valence band of the part of the strontium
niobium oxynitride film 120 in which the light has been absorbed.
Since the strontium niobium oxynitride film 120 is an n-type
semiconductor, the holes migrate to the surface of the strontium
niobium oxynitride film 120.
[0044] Water is split on the surface of the strontium niobium
oxynitride film 120 as shown in the following reaction formula (1)
to generate oxygen. On the other hand, electrons migrate from the
strontium niobium oxynitride film 120 to the counter electrode 630
through the conducting wire 650. Hydrogen is generated as shown in
the following reaction formula (2) on the surface of the counter
electrode 630.
4h.sup.++2H.sub.2O.fwdarw.O.sub.2.uparw.+4H.sup.+ (1) [0045]
(h.sup.+ represents a hole)
[0045] 4e.sup.-+4H.sup.+.fwdarw.2H.sub.2.uparw. (2)
[0046] There is a depletion layer having a band bending on a
solid-liquid interface formed on the surface of the strontium
niobium oxynitride film 120. Theoretically, a depletion layer
extends with a decrease in carrier density. Therefore, in a case
where carrier density is low, electrons and holes generated in the
conduction band and the valence band respectively are easily
separated due to the internal electric field of the depletion
layer. Since the semiconductor photoelectrode 100 according to the
embodiment has low carrier density of less than 1.0.times.10.sup.18
cm.sup.-3, a hydrogen generation device comprising the
semiconductor photoelectrode 100 according to the embodiment has
high hydrogen generation efficiency.
EXAMPLES
[0047] Hereinafter, the present invention will be described in more
detail with reference to the following examples.
Inventive Example 1
[0048] In the inventive example 1, a semiconductor photoelectrode
100 shown in FIG. 1 was fabricated as below.
[0049] First, a strontium niobium oxynitride film 120 having a
thickness of 100 nanometers was grown by a reactive sputtering
method on a perovskite strontium titanate substrate 110 having a
(001) orientation only. In the reactive sputtering method, the
temperature of the strontium titanate substrate 110 was maintained
at 650 degrees Celsius. The material of the sputtering target was
strontium niobate represented by the chemical formula
Sr.sub.2Nb.sub.2O.sub.7. The sputtering was carried out in an
atmosphere of a mixture of argon, oxygen, and nitrogen. The total
pressure in the chamber used for the sputtering was 0.5 Pa. The
flow rate of argon was 5 sccm. The flow rate of oxygen was 0.05
sccm. The flow rate of nitrogen was 10 sccm. In this way, the
strontium niobium oxynitride film 120 was grown epitaxially.
[0050] Then, the carrier density of the strontium niobium
oxynitride film 120 was calculated through the Hall effect
measurement based on the Van der Pauw method. As a result, the
strontium niobium oxynitride film 120 according to the inventive
example 1 had carrier density of 5.5.times.10.sup.15 cm.sup.-3.
[0051] The semiconductor photoelectrode 100 was subjected to an
X-ray diffraction analysis. FIG. 2 shows the result. As is clear
from FIG. 2, six peaks were observed. Among them, three peaks are
derived from a (001) plane, a (002) plane, and a (003) plane of the
SrTiO.sub.3. Other three peaks are derived from a (001) plane, a
(002) plane, and a (003) plane of SrNbO.sub.2N. As just described,
only peaks of (00h) planes of SrNbO.sub.2N were observed. This
means that a strontium niobium oxynitride film having a (001)
orientation only was formed on the strontium titanate substrate 110
having a (001) plane orientation.
Inventive Example 2
[0052] In the inventive example 2, the semiconductor photoelectrode
100 shown in FIG. 1 was fabricated as below. The main difference
from the inventive example 1 is that the atmosphere of the
sputtering did not contain oxygen.
[0053] First, a strontium niobium oxynitride film 120 having a
thickness of 100 nanometers was grown by a reactive sputtering
method on a perovskite strontium titanate substrate 110 having a
(001) orientation only. In the reactive sputtering method, the
temperature of the strontium titanate substrate 110 was maintained
at 650 degrees Celsius. The material of the sputtering target was
strontium niobate represented by the chemical formula
Sr.sub.2Nb.sub.2O.sub.7. The sputtering was carried out in an
atmosphere of a mixture of argon and nitrogen. The total pressure
in the chamber used for the sputtering was 0.5 Pa. The flow rate of
argon was 5 sccm. The flow rate of nitrogen was 10 sccm. In this
way, the strontium niobium oxynitride film 120 was grown.
[0054] Then, the carrier density of the strontium niobium
oxynitride film 120 was calculated through the Hall effect
measurement based on the Van der Pauw method. As a result, the
strontium niobium oxynitride film 120 according to the inventive
example 2 had carrier density of 1.7.times.10.sup.17 cm.sup.-3.
[0055] The semiconductor photoelectrode 100 was subjected to an
X-ray diffraction analysis. FIG. 3 shows the result. As is clear
from FIG. 3, six peaks were observed. Among them, three peaks are
derived from a (001) plane, a (002) plane, and a (003) plane of the
SrTiO.sub.3. Other three peaks are derived from a (001) plane, a
(002) plane, and a (003) plane of SrNbO.sub.2N. As just described,
only peaks of (00h) planes of SrNbO.sub.2N were observed. This
means that a strontium niobium oxynitride film having a (001)
orientation only was formed on the strontium titanate substrate 110
having a (001) plane orientation.
[0056] The following Table 1 shows the results of the inventive
examples 1-2.
TABLE-US-00001 TABLE 1 Inventive Inventive example 1 example 2
Substrate SrTiO.sub.3 substrate having a (001) orientation only
Growth temperature (Celsius) 650 650 Film thickness (nanometer) 100
100 Argon flow rate (sccm) 5 5 Oxygen flow rate (sccm) 0.05 0
Nitrogen flow rate (sccm) 10 10 Orientation (001) only (001) only
Carrier density (cm.sup.-3) 5.5 .times. 10.sup.15 1.7 .times.
10.sup.17
Inventive Example 3
[0057] In the inventive example 3, an experiment similar to the
inventive example 1 was conducted, except that the perovskite
strontium titanate substrate 110 has not a (001) orientation only,
but a (110) orientation only.
Inventive Example 4
[0058] In the inventive example 4, an experiment similar to the
inventive example 1 was conducted, except that the perovskite
strontium titanate substrate 110 has not a (001) orientation only,
but a (111) orientation only.
[0059] The following Table 2 shows the results of the inventive
examples 3-4.
TABLE-US-00002 TABLE 2 Inventive Inventive example 3 example 4
Substrate SrTiO.sub.3 substrate SrTiO.sub.3 substrate having a
(110) having a (111) orientation only orientation only Growth
temperature (Celsius) 650 650 Film thickness (nanometer) 100 100
Argon flow rate (sccm) 5 5 Oxygen flow rate (sccm) 0.05 0.05
Nitrogen flow rate (sccm) 10 10 Orientation (110) only (111) only
Carrier density (cm.sup.-3) 2.1 .times. 10.sup.15 1.8 .times.
10.sup.15
INDUSTRIAL APPLICABILITY
[0060] The strontium niobium oxynitride film according to the
present invention can be used as a semiconductor photoelectrode
used in a hydrogen generation device for generating hydrogen
through light irradiation.
REFERENTIAL SIGNS LIST
[0061] 100 Semiconductor photoelectrode [0062] 110 Strontium
titanate substrate [0063] 111 Ohmic electrode [0064] 120 Strontium
niobium oxynitride film [0065] 600 Hydrogen generation device
[0066] 610 Container [0067] 630 Counter electrode [0068] 640 Liquid
[0069] 650 Conducting wire
CONCLUSION
[0070] The inventions derived from the above disclosure will be
listed below. [0071] 1. A method for growing a strontium niobium
oxynitride film, the method comprising:
[0072] (a) growing, on a strontium titanate substrate, by a
sputtering method, the strontium niobium oxynitride film having
carrier density of not more than 1.times.10.sup.13 cm.sup.-3.
[0073] 2. The method according to Item 1, wherein
[0074] a target used in the sputtering method is formed of
strontium niobate; and
[0075] the strontium niobium oxynitride film is grown in an
atmosphere containing nitrogen. [0076] 3. The method according to
Item 2, wherein
[0077] the strontium niobate is represented by the chemical formula
Sr.sub.2Nb.sub.2O.sub.7. [0078] 4. The method according to Item 2,
wherein
[0079] the atmosphere further contains oxygen. [0080] 5. The method
according to Item 2, wherein
[0081] the atmosphere further contains argon. [0082] 6. The method
according to Item 4, wherein
[0083] the atmosphere further contains argon. [0084] 7. The method
according to Item 1, wherein
[0085] the strontium titanate substrate has a single orientation
plane; and
[0086] the strontium niobium oxynitride film has a single
orientation plane. [0087] 8. The method according to Item 7,
wherein
[0088] the single orientation plane of the strontium titanate
substrate is an orientation plane of a (001) plane; and
[0089] the single orientation plane of the strontium niobium
oxynitride film is an orientation plane of a (001) plane. [0090] 9.
The method according to Item 7, wherein
[0091] the single orientation plane of the strontium titanate
substrate is an orientation plane of a (110) plane; and
[0092] the single orientation plane of the strontium niobium
oxynitride film is an orientation plane of a (110) plane. [0093]
10. The method according to Item 7, wherein
[0094] the single orientation plane of the strontium titanate
substrate is an orientation plane of a (111) plane; and
[0095] the single orientation plane of the strontium niobium
oxynitride film is an orientation plane of a (111) plane. [0096]
11. The method according to Item 1, wherein
[0097] the strontium titanate substrate is doped with at least one
selected from the group consisting of niobium and lanthanum. [0098]
12. A strontium niobium oxynitride having carrier density of not
more than 1.times.10.sup.18 cm.sup.-3. [0099] 13. The strontium
niobium oxynitride according to Item 12, wherein
[0100] the carrier density is not more than 1.times.10.sup.17
cm.sup.-3. [0101] 14. A strontium niobium oxynitride film having
carrier density of not more than 1.times.10.sup.18 cm.sup.-3.
[0102] 15. The strontium niobium oxynitride film according to Item
14, wherein
[0103] the carrier density is not more than 1.times.10.sup.17
cm.sup.-3. [0104] 16. The strontium niobium oxynitride film
according to Item 14, wherein
[0105] the strontium niobium oxynitride film has a single
orientation plane. [0106] 17. The strontium niobium oxynitride film
according to Item 16, wherein
[0107] the single orientation plane is an orientation plane of a
(001) plane. [0108] 18. The strontium niobium oxynitride film
according to Item 16, wherein
[0109] the single orientation plane is an orientation plane of a
(110) plane. [0110] 19. The strontium niobium oxynitride film
according to Item 16, wherein
[0111] the single orientation plane is an orientation plane of a
(111) plane. [0112] 20. A semiconductor photoelectrode
comprising:
[0113] a strontium titanate substrate; and
[0114] a strontium niobium oxynitride film grown on the strontium
titanate substrate,
[0115] wherein
[0116] the strontium niobium oxynitride film has carrier density of
not more than 1.times.10.sup.18 cm.sup.-3. [0117] 21. The
semiconductor photoelectrode according to Item 20, wherein
[0118] the carrier density is not more than 1.times.10.sup.17
cm.sup.-3. [0119] 22. The semiconductor photoelectrode according to
Item 20, wherein
[0120] the strontium titanate substrate has a single orientation
plane; and
[0121] the strontium niobium oxynitride film has a single
orientation plane. [0122] 23. The semiconductor photoelectrode
according to Item 22, wherein
[0123] the single orientation plane of the strontium titanate
substrate is an orientation plane of a (001) plane; and
[0124] the single orientation plane of the strontium niobium
oxynitride film is an orientation plane of a (001) plane. [0125]
24. The semiconductor photoelectrode according to Item 22,
wherein
[0126] the single orientation plane of the strontium titanate
substrate is an orientation plane of a (110) plane; and
[0127] the single orientation plane of the strontium niobium
oxynitride film is an orientation plane of a (110) plane. [0128] 25
The semiconductor photoelectrode according to Item 22, wherein
[0129] the single orientation plane of the strontium titanate
substrate is an orientation plane of a (111) plane; and
[0130] the single orientation plane of the strontium niobium
oxynitride film is an orientation plane of a (111) plane. [0131]
26. The semiconductor photoelectrode according to Item 20,
wherein
[0132] the strontium titanate substrate is doped with at least one
selected from the group consisting of niobium and lanthanum. [0133]
27. A hydrogen generation device, comprising:
[0134] a semiconductor photoelectrode according to Item 20;
[0135] a counter electrode electrically connected to the
semiconductor photoelectrode;
[0136] a liquid in contact with the strontium niobium oxynitride
film and the counter electrode; and
[0137] a container containing the semiconductor photoelectrode, the
counter electrode, and the liquid, wherein
[0138] the liquid is water or an electrolyte aqueous solution;
and
[0139] hydrogen is generated on a surface of the counter electrode
when the strontium niobium oxynitride film is irradiated with
light. [0140] 28. The hydrogen generation device according to Item
27, wherein
[0141] the carrier density is not more than 1.times.10.sup.17
cm.sup.-3. [0142] 29. The hydrogen generation device according to
Item 27, wherein
[0143] the strontium titanate substrate has a single orientation
plane; and
[0144] the strontium niobium oxynitride film has a single
orientation plane. [0145] 30. The hydrogen generation device
according to Item 29, wherein
[0146] the single orientation plane of the strontium titanate
substrate is an orientation plane of a (001) plane; and
[0147] the single orientation plane of the strontium niobium
oxynitride film is an orientation plane of a (001) plane. [0148]
31. The hydrogen generation device according to Item 29,
wherein
[0149] the single orientation plane of the strontium titanate
substrate is an orientation plane of a (110) plane; and
[0150] the single orientation plane of the strontium niobium
oxynitride film is an orientation plane of a (110) plane. [0151]
32. The hydrogen generation device according to Item 29,
wherein
[0152] the single orientation plane of the strontium titanate
substrate is an orientation plane of a (111) plane; and
[0153] the single orientation plane of the strontium niobium
oxynitride film is an orientation plane of a (111) plane. [0154]
33. The hydrogen generation device according to Item 27,
wherein
[0155] the strontium titanate substrate is doped with at least one
selected from the group consisting of niobium and lanthanum. [0156]
34. A method for generating hydrogen, comprising:
[0157] (a) preparing a hydrogen generation device, comprising:
[0158] a semiconductor photoelectrode according to claim 16;
[0159] a counter electrode electrically connected to the
semiconductor photoelectrode;
[0160] a liquid in contact with the strontium niobium oxynitride
film and the counter electrode; and
[0161] a container containing the semiconductor photoelectrode, the
counter electrode, and the liquid,
[0162] wherein
[0163] the liquid is water or an electrolyte aqueous solution;
and
[0164] (b) irradiating the strontium niobium oxynitride film with
light to generate hydrogen on a surface of the counter electrode.
[0165] 35. The method according to Item 34. wherein
[0166] the carrier density is not more than 1.times.10.sup.17
cm.sup.-3. [0167] 36. The method according to Item 34, wherein
[0168] the strontium titanate substrate has a single orientation
plane; and
[0169] the strontium niobium oxynitride film has a single
orientation plane. [0170] 37. The method according to Item 36,
wherein
[0171] the single orientation plane of the strontium titanate
substrate is an orientation plane of a (001) plane; and
[0172] the single orientation plane of the strontium niobium
oxynitride film is an orientation plane of a (001) plane. [0173]
38. The method according to Item 36, wherein
[0174] the single orientation plane of the strontium titanate
substrate is an orientation plane of a (110) plane; and
[0175] the single orientation plane of the strontium niobium
oxynitride film is an orientation plane of a (110) plane. [0176]
39. The method according to Item 36, wherein
[0177] the single orientation plane of the strontium titanate
substrate is an orientation plane of a (111) plane; and
[0178] the single orientation plane of the strontium niobium
oxynitride film is an orientation plane of a (111) plane. [0179]
40. The method according to Item 34, wherein
[0180] the strontium titanate substrate is doped with at least one
selected from the group consisting of niobium and lanthanum.
* * * * *